Welding cast iron can be challenging due to its brittle nature and susceptibility to cracking. There are several welding techniques available, including manual arc welding, gas welding, COâ‚‚ shielded welding, and manual electroslag welding. Manual arc welding is further categorized into hot welding, semi-hot welding, and cold welding, while gas welding includes hot welding, heating and reducing welding, and no preheating welding. The choice of method depends on factors such as the size and thickness of the casting, the condition of the defect, structural complexity, and post-weld requirements like machining, tightness, strength, and color.
In automotive and tractor applications, cylinder blocks often suffer from cracks, holes, or damaged shapes that require welding repair. Common materials used in these components include HT21-4 and HT15-32, which are known for their poor weldability. Combined with the thin and uneven wall structure of the cylinder, this makes welding prone to cracking, thus posing significant challenges during repairs. Considering production efficiency, cost, and practical conditions, manual arc cold welding is frequently preferred. Below are two examples illustrating the process for repairing cylinder blocks.
Case 1: A Dongfeng windmill cylinder had a surface damage caused by disassembly. We replaced the damaged area with low-carbon steel plate and used manual arc cold welding. A 3.2mm diameter cast 308 electrode was employed with a current of 100A. The welding was done in short segments, with intermittent and dispersed passes to minimize stress and prevent cracking.
The defect was located on the surface, so there was no need for extensive machining. If the original block were fully filled, it could increase internal stress and reduce crack resistance. Therefore, we carefully cleaned the area around the defect, annealed the low-carbon steel plate, and only opened a half-side groove around the casting. We used both cast 308 and 506 carbon steel electrodes to ensure quality and reduce costs. Each weld was kept under 20mm in length, and after each pass, the weld was immediately tapped with a small hammer to relieve stress and improve density. Any minor porosity or slag could be minimized through this process without affecting the tensile strength of the weld.
After each weld, the area was cooled to a safe temperature and then cleaned with a wire brush before proceeding to the next section. This process was repeated until the entire repair was completed.
Case 2: A forklift cylinder cracked due to freezing in winter when antifreeze was not used. The crack was 50mm long, with a 5mm protrusion in the middle. To address this, we first flattened the crack using pressure iron and sealed the ends. Given the long crack and high rigidity, we used a 3.2mm cast 308 electrode with a beveled sand wheel. Each weld was 10–15mm long, followed by tapping with a small hammer to relieve stress. After cooling to approximately 600°C, the next segment was welded. Finally, three steel plates measuring 30x50mm and 3mm thick were used to reinforce the welds, ensuring the crack was fully sealed.
Practical experience has shown that the above methods are effective and feasible for cast iron welding, especially for cylinder block repairs. These techniques are recommended for widespread application in industrial settings where cast iron components require reliable and durable welding solutions.
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